A roller cone rock bit is a common cutting tool used in oil, gas, and mining fields for breaking through earth formations and shaping well bores. Reference is made to FIG. 1 which illustrates a partially broken away view of a typical roller cone rock bit. FIG. 1 more specifically illustrates one head and cone assembly. The general configuration and operation of such a bit is well known to those skilled in the art.
The head 1 of the bit includes the bearing shaft 2. A cutting cone 3 is rotatably positioned on the bearing shaft 2 which may function as a journal. A body portion 4 of the bit includes an upper portion that is typically threaded for forming a tool joint connection that facilitates connection of the bit to a drill string (not shown). A lubrication system 6 is included to provide lubricant to, and retain lubricant in, the bearing between the cone 3 and the bearing shaft 2. This system 6 has a configuration and operation well known to those skilled in the art.
The bearings used in roller cone rock bits typically employ either rollers as the load carrying element or a journal (as shown in FIG. 1) as the load carrying element. A number of bearing systems are provided in connection with the bearing supporting rotation of the cone 3 about the bearing shaft 2. These bearing systems include a first cylindrical friction bearing 10 (also referred to as the main journal bearing), ball bearings 12, second cylindrical friction bearing 14, first radial friction (thrust) bearing 16 and second radial friction (thrust) bearing 18.
The first cylindrical friction bearing (main journal bearing) 10 of the bearing system is defined by an outer cylindrical surface 20 on the bearing shaft 2 and an inner cylindrical surface 22 of a bushing 24 which has been press fit into the cone 3. This bushing 24 is a ring-shaped structure typically made of beryllium copper, although the use of other materials is known in the art. The ball bearings 12 ride in an annular raceway 26 defined at the interface between the bearing shaft 2 and cone 3. The second cylindrical friction bearing 14 of the bearing system is defined by an outer cylindrical surface 30 on the bearing shaft 2 and an inner cylindrical surface 32 on the cone 3. The outer cylindrical surface 30 is inwardly radially offset from the outer cylindrical surface 20. The first radial friction bearing 16 is defined between the first and second cylindrical friction bearings 10 and 12 by a first radial surface 40 on the bearing shaft 2 and a second radial surface 42 on the cone 3. The second radial friction bearing 18 is adjacent the second cylindrical friction bearing 12 at the axis of rotation for the cone and is defined by a third radial surface 50 on the bearing shaft 2 and a fourth radial surface 52 on the cone 3.
Lubricant is provided in the first cylindrical friction bearing 10, second cylindrical friction bearing 14, first radial friction bearing 16 and second radial friction bearing 18 between the opposed cylindrical and radial surfaces using the system 6. It is critical to retain the lubricant in positions between the opposed surfaces of the bearing system. Retention of the lubricant requires that a sliding seal be formed between the bearing system and the external environment of the bit.
An o-ring seal 60 is positioned in a seal gland 64 between cutter cone 3 and the bearing shaft 2 to retain lubricant and exclude external debris. A cylindrical surface seal boss 62 is provided on the bearing shaft. In the illustrated configuration, this surface of the seal boss 62 is outwardly radially offset (by the thickness of the bushing 24) from the outer cylindrical surface 20 of the first friction bearing 10. It will be understood that the seal boss could exhibit no offset with respect to the main journal bearing surface if desired (see, for example, FIG. 3). The annular seal gland 64 is formed in the cone 3. The gland 64 and seal boss 62 align with each other when the cutting cone 3 is rotatably positioned on the bearing shaft. The o-ring seal 60 is compressed between the surface(s) of the gland 64 and the seal boss 62, with the o-ring seal 60 sliding on the seal boss surface 62 and functioning to retain lubricant in the bearing area around the bearing systems. This seal also assists in preventing materials (drilling mud and debris) in the well bore from entering into the bearing area.
Early seals for rock bits were designed with a metallic Belleville spring clad with an elastomer, usually nitrile rubber (NBR). A significant advancement in rock bit seals came when o-ring type seals were introduced (see, Galle, U.S. Pat. No. 3,397,928, the disclosure of which is hereby incorporated by reference). These o-ring seals were composed of nitrile rubber and were circular in cross section. The seal was fitted into a radial gland formed by cylindrical surfaces between the head and cone bearings, and the annulus formed was smaller than the original dimension as measured as the cross section of the seal. Schumacher (U.S. Pat. No. 3,765,495, the disclosure of which is hereby incorporated by reference) teaches a variation of this seal by elongating the radial dimension which, when compared to the seal disclosed by Galle, required less percentage squeeze to form an effective seal.
Several other minor variations of this sealing concept have been used, each relying on an elastomer seal squeezed radially in a gland formed by cylindrical surfaces between the two bearing elements, and are well known to those skilled in the art. Over time, the rock bit industry has moved from a standard nitrile material for the seal ring, to a highly saturated nitrile elastomer for added stability of properties (thermal resistance, chemical resistance).
The use of a sealing means in rock bit bearings has dramatically increased bearing life in the past fifty years. The longer the seal excludes contamination from the bearing, the longer the life of the bearing and drill bit. The seal is, thus, a critical component of the rock bit. Indeed, the life of the seal is limited by seal wear and damage. The seal 60 is retained in the gland 64 and slides on the bearing shaft (at surface 62) and functions to separate the grease of the bearing from the outside environment (drilling mud, air, cuttings, etc.). The presence of abrasive particles (known as detritus) introduced to the seal from the outside environment tends to accelerate the wear of the seal 60. For instance, if the abrasive particles are of sufficient size (or quantity), the seal 60 can be torn.
To address this issue, it is known to those skilled in the art to create some sort of convolution 80 in the fluid path between the seal gland and the outside environment. This convolution is created by the geometry of the head and cone. FIG. 1 illustrates one example in a sealed bearing of such a convolution 80 created by configuring the geometry of the head and cone to introduce a corner 82 (formed in this case by a right angle) in the fluid path between the seal 60 and the outside environment 84. FIG. 2 illustrates another example of such a convolution 80 in a sealed bearing created by configuring the geometry of the head and cone to introduce two corners 86 and 88 (each formed in this case by an obtuse angle, although right angles or mixed angles could be used) in the fluid path between the seal 60 and the outside environment 84. An additional corner 82 (formed in this case by an obtuse angle, although a right angle could be used, and positioned similarly to the single corner shown in FIG. 1) is also provided in the fluid path. FIG. 3 illustrates another example of such a convolution 80 created by configuring the geometry of the head and cone to introduce two corners 86 and 88 (each formed in this case by an obtuse angle, although right angles or mixed angles could be used) in the fluid path between the seal 60 and the outside environment 84. The included convolution 80 functions to impede the passage of abrasive particles (detritus) from the outside environment 84 towards the seal 60.
Reference is now made to FIG. 4 which shows the use of a labyrinth seal protector 90 in a sealed bearing to introduce the convolution 80 in the fluid path between the seal 60 and the outside environment 84. The labyrinth seal protector 90 is a ring structure having an L-shape (in cross-section). An annular groove 92 is formed in a radial base surface 91 of the cone 3. The annular groove 92 is radially offset from the seal gland by surface 94. The shorter leg of the L-shaped labyrinth seal protector 90 ring is inserted into the annular groove 92, with the longer leg of the L-shaped labyrinth seal protector 90 ring positioned between the cone 3 (surface 91) and the radial base surface 93 of the head 1 adjacent the shaft 2. Reference is made to Shotwell, U.S. Pat. No. 4,613,004, the disclosure of which is hereby incorporated by reference.
Reference is now additionally made to FIG. 5. The labyrinth seal protector 90 divides the fluid path between the seal 60 and the outside environment 84 into a first fluid path 300 extending around the surfaces of the annular groove 92 and surface 94 (passing corners 95, 96, 97 and 98) and a second fluid path 302 extending along the radial base surface 93 of the head 1 adjacent the shaft 2 and the cylindrical surface 62 (passing corner 82). The dotted lines in FIG. 5 generally illustrate the surfaces of the head, shaft and cone adjacent the protector 90 and seal 60. The first and second fluid paths 300 and 302 are parallel to each other with respect to passing around the L-shaped labyrinth seal protector 90 ring. Notwithstanding the introduction of a convolution 80 in the first fluid path 300 requiring passage by four corners (95, 96, 97 and 98), the configuration of FIG. 4 still presents a second fluid path 302 having a convolution 80 with only a single corner (82).
There is a need for an improved labyrinth seal protector structure and configuration which provides for better protection against the passage of abrasive particles (detritus) from the outside environment 84 towards the seal 60.
It is also known in the art to have an open bearing (i.e., a non-sealed bearing which does not use a sealed lubricant) in some applications. The open bearing may comprise either a journal bearing or a roller bearing, or some combination of bearing structures and systems. The issue of excluding contamination from the bearing, so as to prolong bearing life, is also a concern with an open bearing. Thus, there is a need in the art for an improved labyrinth protector structure and configuration which provides for better protection against the passage of abrasive particles (detritus) from the outside environment towards the bearing structure.
Reference is further made to the following prior art references (the disclosures of all references are incorporated herein by reference): U.S. Pat. Nos. 3,656,764, 4,102,419, 4,179,003, 4,200,343, 4,209,890, 4,613,004, 5,005,989, 5,027,911, 5,224,560, 5,513,715, 5,570,750, 5,740,871, 6,254,275, and 7,798,248, and U.S. Patent Application Publication No. 2010/0038144.